The introduction in recent years of a multitude of new fluorescent dyes to measure cellular and subcellular events has lead to an increasing demand for high performance fluorometers. Fluorometers currently available to the research community often have limited wavelength selection, slow response, poor spectral purity, large background signals, and are quite expensive. Many of these limitations are due to the use of monochromators to select photon wavelength. The general aim of this proposal is to develop a fluorometer that eliminates the expense and limitations of monochromators, and provide the scientific community with an instrument that is considerably more versatile and considerably less expensive. The specific aims of this phase I proposal are: 1. To prototype a digitally controlled fluorometer with low noise characteristics, multiwavelength excitation and emission modes, high spectral purity, and 2 ms data acquisition rate. This prototype will also eliminate the expense and limitations of monochromators. 2. To facilitate design simplicity and reduce expense by incorporating all of the hardware for the computer interface and data acquisition onto a single resident PC card. The lower cost of this substantially more versatile fluorometer will make the technology available to many researchers in this rapidly developing field, and accelerate the application of fluorescent techniques and our understanding of subcellular processes.